Discussion on: AoC Day 2: Inventory Management System

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace Day2Part1
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] inputTxt = File.ReadAllLines(@"C:\Users\Ben\Desktop\adventOfCode2018\Day 2\input.txt");
            List<int> TwoMatchList = new List<int>();// List of id's to find box in the input array
            List<int> ThreeMatchList = new List<int>();// list of id's to find box in the input array
            foreach (string boxID in inputTxt)
            {
                int id = Array.IndexOf(inputTxt, boxID);
                var distinctLetters = boxID.Select(x => x).Distinct().ToList();
                foreach (char letter in distinctLetters)
                {
                    var matches = boxID.Where(x => x == letter).ToList();
                    switch (matches.Count)
                    {
                        case 2:
                            //if there's exactly 2, and it's not already in the list then add it to the TwoMatchList
                            if (!TwoMatchList.Contains(id))
                            {
                                TwoMatchList.Add(id);
                            }
                            break;
                        case 3:
                            //if there's exactly 3, and it's not already in the list then add it to the ThreeMatchList
                            if (!ThreeMatchList.Contains(id))
                            {
                                ThreeMatchList.Add(id);
                            }
                            break;
                        default:
                            //don't add to any list
                            break;
                    }//end switch
                }//end foreach letter
            }//end foreach boxID
            int checksum = TwoMatchList.Count * ThreeMatchList.Count;
            Console.WriteLine("Number of boxes with exactly two matching letters {0}", TwoMatchList.Count);
            Console.WriteLine("Number of boxes with exactly three matching letters {0}", ThreeMatchList.Count);
            Console.WriteLine("Checksum: {0}", checksum);
            Console.WriteLine();


            Console.WriteLine("Now for part two!");

            //empty Dictionary to hold any boxes we find and the index of the letter that's different
            Dictionary<string, int> savedIDsAndIndexes = new Dictionary<string, int>();

            //empty string to hold the answer
            string answer = "";

            //Loop through to test and find correct boxes ==>> this could be a foreach loop
            for (int i = 0; i < inputTxt.Length; i++)
            {
                string boxID = inputTxt[i];
                for (int j = inputTxt.Length - 1; j >= 0; j--)
                {
                    List<int> mismatchIndexes = new List<int>();
                    string testBoxID = inputTxt[j];
                    for (int k = 0; k < boxID.Length; k++)
                    {
                        if (boxID[k] != testBoxID[k])
                        {
                            mismatchIndexes.Add(k);
                        }
                    }
                    if (mismatchIndexes.Count == 1)
                    {
                        savedIDsAndIndexes.Add(boxID, mismatchIndexes.First());
                    }
                }
            }

            Console.WriteLine("number of correct boxes found: {0}", savedIDsAndIndexes.Count);

            answer = savedIDsAndIndexes.Keys.First().Substring(0, savedIDsAndIndexes.Values.First())
                + savedIDsAndIndexes.Keys.First().Substring(savedIDsAndIndexes.Values.First() + 1);

            Console.WriteLine("here are the ids:");
            foreach (var id in savedIDsAndIndexes)
            {
                Console.WriteLine(id.Key);
            }

            Console.WriteLine("The common characters are:\n{0}", answer);

            Console.WriteLine("saved index: {0}", savedIDsAndIndexes.Values.First());
        }
    }
}